A major interest in geriatrics and gerontology is the relationship between disease, impairment, functional performance and disability. The variability in disability in the elderly cannot be fully explained by disease specific diagnoses and the relationship between impairments and functional performance is not fully understood. There are many issues and problems specific to assessment of the relationship between impairments, functional limitations, and disability. First, there are few well characterized measures of these variables. Second, the feasibility and practicality of collecting quality of life measures in the elderly is not well defined. Third, there is rarely a single specific deficit that contributes to functional decline in the elderly, but there are a myriad of factors that contribute, some of which are rarely considered (i.e., axial mobility and strength). In addition, the relationship between impairments and functional performance may be best explained by an accumulation of deficits rather than a single specific impairment. Finally, limited information is available on the biomechanical effects of limited axial mobility and strength. To address these issues in this OAIC proposal, we have proposed a core which will focus on the measurement and biomechanics of limited mobility. Models will be developed based on the measured cross-sectional data to attempt to explain the variation in functional performance and disability. This core will bring together epidemiologists, sociologists, engineers, and physical therapists to address these issues. The core will offer four levels of contributions: 1) basic support to train all data collectors, 2) research to establish test characteristics of all measures employed, 3) research to explain variation in functional performance and disability among a diverse group of subjects, and 4) biomechanical analysis of the effects of axial dysmobility.